The invention relates generally to carburetors, and more particularly to carburetors of the membrane type.
It is known that carburetors of the membrane type, unlike other types of carburetor, were designed for the purpose of assuring correct operation or the optimum fueling of an internal combustion engine, even when the engine is used in positions ranging from its proper horizontal position to the inverted position.
The membrane carburetors referred to above are used particularly in portable chain saws and in outboard motors on any kind of boats, and in general in all cases in which the internal combustion engine is mounted on machines, devices and equipment which, on account of their particular use, are subjected to constant rocking, tilting or shifting of position. In brief, the membrane carburetors of the known type are essentially provided centrally with a Venturi tube through which air passes to constitute the combustible mixture, and within which the high-speed and idle jets terminate. These jets are connected by appropriate passages, with the interposition of suitable regulating screws, to a fuel accumulating chamber which is supplied by a conventional diaphragm pump. One surface of said diaphragm pump is in contact with the fuel which is drawn from the fuel tank, while the opposite surface faces a chamber which receives the drive pulses from the crank-case of the internal combustion engine.
Furthermore, for the proper operation of the motor, the outside wall of the fuel accumulating chamber is defined by a thin membrane which is connected, through the medium of a suitable rocker arm, to the needle valve which is interposed between the diaphragm pump and the above-mentioned fuel accumulating chamber.
Lastly, the surface of the said membrane which is external to the fuel accumulating chamber is directly in contact with the atmosphere so as to operate at atmospheric pressure, and it is for this reason that this membrane is often called the "compensating membrane."
Although the membrane carburetors of the type treated above, and thus structured and designed, have proven and still prove to be suitable for the uses for which they are intended, they have serious deficiencies, particularly when they must operate under adverse conditions, and more particularly when they are partially or completely submerged in a liquid, which can be, for example, water. In fact, if the internal combustion engine is to operate partially or completely submerged, as for example in the case of a means of propulsion for an underwater exploration or working machine, in the case of a chain saw to be used in cutting up tree trunks obstructing the banks of a river, in the case, which is often encountered, of operation in a heavy downpour of rain, in the case of outboard motors in general, in the case of a traction and transport means for an underwater explorer or SCUBA diver, and in all cases in which it is required, the compensating action of the carburetor membrane will fail because there is added to the atmospheric pressure, which is optimum for the proper operation of the carburetor, the hydrostatic head, which is defined by the difference in altitude between the free surface of the fresh or salt water or other liquid and the depth reached in this liquid by the said compensating membrane.
The difficulties cited above result, of course, in the complete stoppage of the engine, with the consequences resulting particularly if the internal combustion engine is a propulsion means for an underwater exploration or working machine, or if it is an outboard motor in a boat which is at sea under particularly adverse conditions.
Furthermore, the above-cited difficulties are worsened by the fact that the compensating action of the membrane is further impaired by the relative movements which take place between the liquid and the membrane due to the movement of the internal combustion engine relative to the liquid, or on account of the movement of the said liquid with respect to the virtually stationary engine; that is to say, in this case, there is added to the atmospheric pressure a hydrodynamic head which, of course, is greater than the hydrostatic head. Furthermore, these difficulties become much more evident in the case of liquids of greater specific gravity, such as salt water or muddy water, industrial liquids or industrial waste liquids which, in comparison with fresh water, present a hydrostatic or hydrodynamic head that is certainly greater than that of fresh water.
In view of what is said above, it certainly is not necessary to direct attention to all the consequences which result from the above-stated difficulties and which result in the stoppage of the internal combustion engine.
In a pending application, Ser. No. 002,041 filed Jan. 5, 1979, now U.S. Pat. No. 4,230,646, a device is disclosed particularly adapted for carburetors of the compensating membrane type for eliminating the difficulties cited above and assuring the proper operation of the internal combustion engine even when the latter is partially or completely immersed in any liquid, particularly water.
The basic concept of that device is to provide a compensating air bag or chamber, connected to a conventional compensating membrane of the carburetor, which will be disposed inside of the internal combustion engine or externally thereof, so as to be reliably influenced only by the atmospheric pressure, maintained in a natural or artificial manner, which is the optimum pressure for the correct operation of the internal combustion engine.
It has been found, however, if atmospheric pressure is not freely communicated to the atmospheric side of the compensating membrane, that is to say if there is any blockage such as any liquid or solid of sufficient quantity and quality to restrict the free flow of compensating atmospheric pressure within any part of the chamber formed around the compensating membrane, it will lose its ability to compensate for the varying pressures on the fuel side thereof and thereby will cause the inlet control needle of the carburetor to open and close out of harmony with the demands of the engine. This situation, depending on the degree of blockage, will cause the engine performance to deviate from normal in degrees from erratic loss of power due to slightly more fuel flow than what is required, to complete engine shutdown due to, most often, a profuse fuel flow and subsequent flooding or conversely a stoppage of fuel flow.
If the above-mentioned blockage occurs, the remedy, in most cases, involves removal, partial disassembly, reassembly, reinstallation and pressure testing the carburetor and its appendages. This procedure requires diagnosis and some degree of technical ability, as well as some special tools.